bp_notifications_get_registered_components()

function bp_notifications_get_registered_components() {

	// Load BuddyPress.
	$bp = buddypress();

	// Setup return value.
	$component_names = array();

	// Get the active components.
	$active_components = array_keys( $bp->active_components );

	// Loop through components, look for callbacks, add to return value.
	foreach ( $active_components as $component ) {
		if ( !empty( $bp->$component->notification_callback ) ) {
			$component_names[] = $component;
		}
		// The extended profile component is identified in the active_components array as 'xprofile'.
		// However, the extended profile child object has the key 'profile' in the $bp object.
		if ( 'xprofile' == $component && ! empty( $bp->profile->notification_callback ) ) {
			$component_names[] = $component;
		}
	}

	/**
	 * Filters active components with registered notifications callbacks.
	 *
	 * @since BuddyPress 1.9.1
	 *
	 * @param array $component_names   Array of registered component names.
	 * @param array $active_components Array of active components.
	 */
	return apply_filters( 'bp_notifications_get_registered_components', $component_names, $active_components );
}